Appsync dynamodb request mapping - default variables - amazon-web-services

Question

I'm looking a way for setting default variables for appsync dynamodb resolvers, if one of variables from query is not provided.
Let's say we have simple db request mapping
{
"version" : "2017-02-28",
"operation" : "PutItem",
"key" : {
## If your table's hash key is not named 'id', update it here. **
"id" : { "S" : "$utils.autoId()" }
},
"attributeValues" : {
## Add an item for each field you would like to store to Amazon DynamoDB. **
"key" : { "S" : "${context.arguments.id}" },
"name" : { "S" : "${context.arguments.name}" }
}
}
I found a way to do this using conditional statements
{
"version" : "2017-02-28",
"operation" : "PutItem",
"key" : {
## If your table's hash key is not named 'id', update it here. **
"id" : { "S" : "$utils.autoId()" }
},
"attributeValues" : {
## Add an item for each field you would like to store to Amazon DynamoDB. **
"key" : { "S" : "${context.arguments.id}" },
#if( ($context.arguments.name))
"name" : { "S" : "${context.arguments.name}" }
#else
"name" : { "S" : "default" }
#end
}
}
Above way we can also exclude one of attributes if it is not provided
{
"version" : "2017-02-28",
"operation" : "PutItem",
"key" : {
## If your table's hash key is not named 'id', update it here. **
"id" : { "S" : "$utils.autoId()" }
},
"attributeValues" : {
## Add an item for each field you would like to store to Amazon DynamoDB. **
"key" : { "S" : "${context.arguments.id}" },
#if( ($context.arguments.name))
"name" : { "S" : "${context.arguments.name}" }
#end
}
}
If $context.arguments.name is not provided then name attribute isn't inserted into dynamodb.
But is there any smarter way to do above?

Answer 1

If you don't want to specify keys explicitly, you can do something like:
{
"version" : "2017-02-28",
"operation" : "PutItem",
"key" : {
## If your table's hash key is not named 'id', update it here. **
"id" : { "S" : "$utils.autoId()" }
},
#set( $expValues = {} )
#foreach( $entry in $context.arguments.entrySet() )
$!{expValues.put("${entry.key}", { "S" : "${entry.value}" })}
#end
#if( !${expValues.isEmpty()} )
"attributeValues" : $utils.toJson($expValues)
#end
}